Two Orcas named Port and Starboard are believed to be behind yet another attack that killed a great white shark after the carcass of a 3.6 metre washed ashore on Saturday 4 July at De Gruis in Gansbaai.
Port and Starboard made international headlines in May 2017 when they were linked to the killing of several great whites, as well as numerous sevengill sharks along our coastline. In February this year they were responsible for the killing of a copper shark (also known as bronze whaler shark).
According to Wilfred Chivell, CEO of Marine Dynamics, the Marine Dynamics/Dyer Island Conservation Trust (DICT) team was notified by resident Paul de Villiers of a white shark stranding.
“We recovered the carcass and transported it to the International Marine Volunteer Lodge where the following morning a team lead by DICT marine biologists collected detailed measurements, photographic, and biological samples.
“The white shark was a 3.6 metre female with a large tear between the two pectoral fins, with the liver and heart missing – identical injuries to those previously recorded on dead white sharks in Gansbaai, and other shark species found along the coast,” said Chivell.
Two days earlier there were confirmed sightings in False Bay of the notorious orca pair. The carcass also showed signs of multiple shark bites along its pelvic area, probably a result of scavenging after the initial predation.
“There were no signs that fishing gear was responsible for the death and no tag was observed on the shark. The DICT team took multiple samples, including fin clippings, muscle, vertebrae, gills and jaws. There has been much speculation regarding the disappearance of white sharks from Gansbaai over the past three years – and what has caused their absence.
“We believe that commercial overfishing and removal of prey species has a critical impact on the number of white sharks and we are encouraged by the recent selection of an expert panel of scientists to advise the Department of Environmental Affairs, Forestry and Fisheries on how to address this matter. However, the impact of orca predations on white sharks in Gansbaai is simply undeniable.
“It is not a smoke screen for a bigger issue but can be linked to pressures other marine species are enduring, adding further urgency to the action on threats affecting the decline of shark stocks along the South African coast,” said Chivell.
According to him the shark cage diving industry is key to daily monitoring of white sharks that can ultimately advise conservation policy. “We have been proactive in setting up our Covid safety protocols so we now await confirmation from government as to when we can start operating.”
Shark biologist Alison Towner comments, “We have monitored the behaviour and abundance of white sharks in the area for over 13 years through an established long-term, boat-based and -tagging data programme. The interactions between orcas and white sharks were first observed in 2017 and seem to occur at similar times each year.
“Although we are only seeing the shark carcasses that wash out, they are all notably larger white sharks, over 3 metres in length. This is concerning for a species that does not reach reproductive maturity until it has exceeded this size. Collaboration between key experts, scientists, and stakeholders is paramount to pro-actively preserve the future diversity of Southern African shark populations,” said Towner.